Security tightened in wake of Berlin attack

Cities across the United States are tightening security following Monday's deadly truck attack at a Berlin Christmas market.

(NBC News) Monday’s attack on a Berlin Christmas market has U.S. security officials on heightened alert.

Extra precautions are being taken to prevent similar truck attacks in cities across the country.

“We’ll make sure the proper barriers are up,” Boston Mayor Marty Walsh said Tuesday. “It’s just a really sad situation.”

In November the State Department warned Americans traveling abroad to be extra careful, and are repeating that warning after Berlin.

“To be vigilant when they are overseas, particularly in Europe, and particularly at public events like festivals in markets, just be self-aware,” says State Department Spokesman Admiral John Kirby.

For the past seven years, ISIS and Al Qaeda have been promoting truck attacks in crowded places.

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